The long-term objective of this research is to elucidate the neurochemical circuitry within the vertebrate retina. Attention will be given to the localization of glutamate receptor molecules at defined synaptic sites with the goal of understanding of how these receptors contribute to the vital task of information processing within the retina. Pre-embedding and post-embedding immunocytochemical techniques will be used to visualize subunits of ionotropic receptors (AMPA-, KA-, and NMDA-selective classes) as well as the metabotropic glutamate receptors in the cat retina. Double-labeling methods will be used to determine the association of subunits within a receptor class and the positioning of receptor classes at synaptic contacts. Co-localizations of subunits from within a receptor class will provide an indication of possible heteromeric assembly at the labeled sites and the positioning of receptors at the synapse has important implications regarding the availability of glutamate for their activation. Other experiments will utilize intracellular filling of individual bipolar and ganglion cells in combination with receptor immunocytochemistry to characterize the sets of glutamate receptor molecules that mediate specific cell to cell contacts. These studies will test the hypothesis that each subpopulation of bipolar cell maintains its specificity within the inner plexiform layer by contacting a unique set of receptors on its target cells and the corollary, that ganglion cells distinguish among inputs from multiple types of bipolar cells on the basis of differences in receptor content at the post-synaptic sites.